The invention relates to a heat exchanger, in particular for a motor vehicle, as well as a method for its manufacture.
The invention more particularly relates to a heat exchanger comprising at least one manifold and at least one fixing lug for each manifold. The fixing lug comprises a concave contact zone, of a shape adapted to the positioning of the said fixing lug on an outer peripheral surface of the manifold, and an attachment zone that extends radially outward from the manifold.
A heat exchanger may form, for example, a condenser that is capable of forming part of an air conditioning installation for a motor vehicle.
A heat exchanger typically is fixed, by means of its fixing lugs, to the environment which surrounds it. In the particular case of an air conditioning condenser, it is habitually fixed either to the structure of the vehicle or to the cooling radiator of the engine of the vehicle.
Conventionally, the fixing lugs and the manifold are metallic and joined by welding in an atmosphere of an inert gas. But such a welding operation has a series of drawbacks: it is expensive, it requires a qualified operator, it can only be performed at a low speed that is inadequate on an industrial scale, and moreover the quality of the resultant joint is unsatisfactory.
The production of the joint by soldering is also known, which necessitates the provision of means to retain and index the fixing lugs on the heat exchanger before and during the soldering operation, which is performed in a suitable furnace.
Known, in particular from document EP-0 440 400, is a heat exchanger of the above-mentioned type, which comprises a heat exchanger body and fixing devices that are fixed to the heat exchanger body. The heat exchanger body comprises flat tubes and fins that are stacked alternately, as well as two hollow manifolds to which the ends of the flat tubes are connected in fluid communication.
The fixing devices illustrated in the above mentioned document each comprise a contact portion, of concave shape, fitting to the outer peripheral surface of a manifold and placed in close contact with the manifold, as well as a fixing portion that extends outwardly from one end of the concave portion and forms a bent-back hook.
The above-mentioned document discloses that this bent-back hook is inserted between two adjacent tubes so that the fixing devices are welded to the body of the heat exchanger and are made integral with the heat exchanger.
In a refinement described in the above-mentioned document, a hole is pierced in the hollow manifold, whereas the fixing lug is punched so as to force back material and form a centring cone in the hole produced in this manner. In another refinement, a hole is pierced in the fixing lug and it is the hollow manifold which is punched.
The heat exchanger according to the above-mentioned document has a certain number of drawbacks. The fixing lug is susceptible to undesirable micro-displacements which can cause poor tightness as well as burrs at the moment of welding. Moreover, the presence of perforations either in the manifold or in the fixing lug may result in leaks and/or infiltrations. Furthermore, the necessity for an anchoring hook to limit the displacements in relation to the fixing lug and the manifold before the welding operation complicates the production of the fixing lug and its assembly.
The object of the invention is particularly to overcome the above-mentioned drawbacks.
In particular it relates to procuring a heat exchanger in which the or each fixing lug may be pre-fitted and kept in a precise position before and during the permanent assembly operation that is performed by soldering or welding.
For this purpose the invention proposes a heat exchanger of the type defined in the introduction, in which the concave contact zone of the fixing lug has a central region of reduced thickness in relation to the normal thickness of the fixing lug, so as to produce a mechanical linkage by clinching, joining the concave contact zone of the fixing lug to the outer peripheral surface of the manifold.
Thus, the fixing lug is pre-fitted to the manifold by a so-called clinching operation, performed by drawing and pressing.
This clinching produces a mechanical linkage by cooperation between the shapes of the manifold and the fixing lug. It permits perfect retention and indexing before and during the furnace soldering operation. The risk of micro-displacements is thus avoided in a particularly effective manner.
Furthermore, this operation may be performed particularly quickly, without requiring a piercing stage as in the prior art.
According to yet another characteristic of the invention, the manifold of the heat exchanger has, in the concave contact zone with the fixing lug, a blind recess delimited by an upper base which is connected to a lateral wall of the recess by a concave shoulder over a chosen depth.
The fixing lug preferably comprises at least one hole previously made to facilitate the subsequent production of the central region of reduced thickness, thanks to the fact that the material of the lug will partially fill this hole whilst limiting the deformation of the lug.
The invention applies in particular to a heat exchanger comprising two manifolds and at least one fixing lug for each manifold.
Such a heat exchanger may be produced in particular in the form of a condenser.
From another angle, the invention relates to a method for the manufacture of such a heat exchanger comprising, for each fixing lug, the steps comprising positioning the said concave contact zone of the fixing lug on the outer peripheral surface of a manifold, then clinching the fixing lug onto the manifold, and finally permanently joining the assembly, for example by furnace soldering.